Heretofore, the intake and exhaust valves of automotive OHC (overhead camshaft) engines are opened and closed by the rotation of the crankshaft that is transmitted through a valve operating apparatus.
Some valve operating apparatus are capable of not only opening and closing the intake and exhaust valves at a predetermining timing with a predetermined lift, but also selectively varying the timing and the lift. The valve operating apparatus with such a mechanism for selecting valve operating modes can control the valve overlap, etc., for optimum values depending on the operating conditions of the engine, so that the engine can produce the highest possible output power at all times.
More specifically, one known valve operating apparatus has a low-speed cam having a cam profile for a low-speed range of operation of the engine, and a high-speed cam having a cam profile for a high-speed range of operation of the engine, the low- and high-speed cams being mounted on a camshaft. The timing to open and close the valves of the engine is controlled by the low-speed cam in the low-speed range of operation, and by the high-speed cam in the high-speed range of operation.
FIGS. 38 through 40 of the accompanying drawings show a mechanism for selecting high- and low-speed cams.
As shown in FIG. 38, rocker arms 104, 105, 104' are interposed between cams 102, 103, 102' and valves 101 to be actuated by the cams.
The cams 102, 102' serve as low-speed cams, and the cam 103 as a high-speed cam. The rocker arms 104, 104' are low-speed rocker arms that are actuated by the cams 102, 102', respectively, and the rocker arm 105 is a high-speed rocker arm that is actuated by the cam 103.
The rocker arms 104, 105, 104' are angularly movably supported on a rocker shaft 106, and angularly movable about the rocker shaft 106 when they are pushed by the cams 102, 103, 102'.
The low-speed rocker arms 104, 104' and the high-speed rocker arm 105 can be engaged or disengaged by pistons 107, 108 and a stopper 109.
More specifically, as shown in FIGS. 39 and 40, the pistons 107, 108 and the stopper 109, which are arranged in series with each other and held in contact end to end, are disposed in cylinders 104a, 105a, 104'a that are defined coaxially in the rocker arms 104, 105, 104', respectively. The rocker shaft 106 and the rocker arm 104' have oil passages 106a, 104'b defined respectively therein. When oil is supplied through the oil passages 106a, 104'b into a space in an end of the cylinder 104'a, the pistons 107, 108 and the stopper 109 are axially moved forwardly, thereby connecting the low-speed locker arms 104, 104' and the high-speed rocker arm 105 to each other. When the oil is discharged, the pistons 107, 108 and the stopper 109 are retracted under the bias of a return spring 110, thereby disconnecting the low-speed rocker arms 104, 104' and the high-speed rocker arm 105 from each other.
The rocker arm 105 is normally urged upwardly by a return spring 111.
In the low-speed range of operation, as shown in FIG. 39, the oil is discharged from the space in the end of the cylinder 104'a, allowing the pistons 107, 108 and the stopper 109 to move to the right under the force of the return spring 110. The piston 107 is placed in the rocker arm 104', the piston 108 in the rocker arm 105, and the stopper 109 in the rocker arm 104. Therefore, the high-speed rocker arm 105 and the low-speed rocker arms 104, 104' are disconnected from each other.
The cam profile of the low-speed cams 102, 102' is now effective to actuate the valves 101.
In the high-speed range of operation, as shown in FIG. 40, the oil is supplied into the space in the end of the piston 104'a to displace the pistons 107, 108 and the stopper 109 to the left under the oil pressure.
The pistons 107, 108 are now positioned such that they connect the low-speed rocker arms 104, 104' and the high-speed rocker arm 105.
The cam lift provided by the high-speed cam 103 is larger than the cam lift provided by the low-speed cams 102, 102' (see FIG. 10). Therefore, the valves 101 are actuated by the high-speed cam 103 while the low-speed cams 102, 102' are idly rotating.
The above conventional valve operating apparatus suffer some problems, to be solved by the present invention, as follows:
When the rocker arms 104, 104', 105 are to be interconnected, two steps of operation are required, i.e., the piston 107 pushes the piston 108, and the piston 108 pushes the stopper 109. At this time, the peripheral edge of the leading end of the piston 107 tends to strike the rocker arm 105 or to be bounced back by the rocker arm 105, and the peripheral edge of the leading end of the piston 108 tends to be bounced back by the rocker arm 104.
When the piston 108 is bounced back, the piston 107 is also bounced back by the piston 108. These pistons 107, 108 are then moved back again to connect the rocker arms 104, 104', 105.
The aforesaid drawback is caused because the rocker arms for reciprocally moving the valves need to be interconnected. The rocker arms 104, 104', 105 cannot smoothly be connected, and the leading ends of the pistons 107, 108 are liable to get worn rapidly.
In addition, since the above connecting mechanism is mounted in the ends of the angularly movable rocker arms, the valve operating apparatus is relatively large in size and weight, and cannot incorporate roller bearings therein.